Method for forming a relative placement of components of an integrated circuit using a structural similarity group

ABSTRACT

A method for forming a structural similarity group from a netlist for use in performing a relative placement of components of an integrated circuit is described. Also described are a method for forming a relative placement of components of an integrated circuit using a structural similarity group and a method for modifying a relative placement of components of an integrated circuit by analyzing adjacent components for shared resources. In addition, methods for determining bus line routing, control line routing, and cleanup line routing for components of an integrated circuit are described.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to processes for determining a layoutfor an integrated circuit from a netlist representing the circuit.

2. Description of Related Art

The rapid transition to a very deep submicro (VDSM) silicon process hascreated a significant demand for a change in design practices within theintegrated circuit (IC) community. As process geometries are gettingsmaller, the functionality that can be packed onto a single chip isincreasing. The VDSM process enables designs measured in tens ofmillions of transistors. As the complexity of integrated circuitsincreases, the time required to lay out the circuity is dramaticallyincreasing. To handle this level of complexity, designers are movingrapidly to a structured, hierarchical design implementation.

Full-custom integrated circuit layout is one of the last frontiers to beconquered by automation and is required to meet the increasing demandsbeing made on custom designers. There is a need for tools to reducedesign time for full custom blocks from months to weeks and even days,while maintaining the quality and performance of manual designs.

Furthermore, the time is rapidly approaching when manual full-customintegrated circuit layout schedules and time-to-market demands will becolliding. As consumer applications become the primary customer for theintegrated circuit industry, time-to-market and design costs will be theprimary design constraints. High quality automated layout solutions areneeded to compete in this new consumer application environment.

While time-to-market concerns is rapidly becoming a critical designparameter, layout optimization in regard to area and performance remainscritical. A need still exists for high quality automated layoutsolutions which can achieve compaction and performance levels that meetor exceed those achievable by manual layout.

Current automation tools appear to be cell-centric, regardless of thefact that interconnect parasitics dominate performance in deepsub-micron designs. As a further layer of impediment to the automationprocess, universal libraries are forced upon all designs, compromisingarea, timing, and power. Interconnect problems are dealt with in areactive mode, since the automation or manual mentality provides minimalcapability for interactive improvements.

A need therefore exists for an automated design tool that can produceintegrated circuits with the density and performance of manual “fullcustom” design, and with the time to market and design throughput of themost efficient “semi-custom” design. These and other needs are addressedby the methods of the present invention.

SUMMARY OF THE INVENTION

A computer implemented method is provided for forming a structuralsimilarity group from a netlist of an integrated circuit comprising:

taking a netlist representation of components forming all or part of anintegrated circuit;

forming groups of the components included in the netlist representationwhich have at least a selected degree of structural similarity betweeneach other; and

forming a structural similarity group which includes those groups ofcomponents identified as having at least the selected degree ofstructural similarity.

A computer implemented method is also provided for forming a relativeplacement of components of an integrated circuit from a netlistcomprising:

taking a netlist representation of components forming all or part of anintegrated circuit;

forming groups of components within the netlist which have at least aselected degree of structural similarity between each other, thosecomponents within the netlist which do not have at least the selecteddegree of structural similarity being omitted from the groups ofcomponents formed;

performing an initial relative placement of the groups of components;

reducing wire lengths between components of initial relative placement;and

adding to the relative placement those components from the netlist whichwere not included in the groups of components.

A computer implemented method is also provided for modifying a relativeplacement of components of an integrated circuit comprising:

taking a relative placement of components of an integrated circuit;

analyzing adjacent components for resources associated with thecomponents which can be shared; and

modifying the relative placement of components such that adjacentcomponents share identified sharable resources.

A computer implemented method is also provided for determining at leastpart of a bus line routing for each bus line of an integrated circuit,each bus line routing including an initial routing and a cleanuprouting, the method comprising:

taking a finalized relative placement of components of the integratedcircuit, the placement including routing constraints and at least afirst and second port locations associated with each bus line;

determining a routing order for the bus lines based on at least onecriterion; and

determining an initial routing for each bus line based on the placement,each initial routing being substantially straight and substantiallyparallel to a bus line axis, a length of each initial routing based on adistance along the bus line axis between the first and second portlocations, a position of each initial routing based on an averagedistance orthogonal to the bus line axis between at least the first andsecond port locations, wherein the placement is unaltered.

A computer implemented method is also provided for determining at leasta part of a control line routing for each control line of an integratedcircuit, each control line routing including an initial routing and acleanup routing, the method comprising:

taking a finalized relative placement of components of the integratedcircuit, the placement including routing constraints and at least afirst and second port locations associated with each control line; and

determining an initial routing for each control line based on theplacement, each initial routing being substantially straight andsubstantially parallel to a control line axis, a length of each initialrouting based on a distance along the control line axis between thefirst and second port locations, a position of each initial routingbased on an average distance orthogonal to the control line axis betweenat least the first and second port locations, wherein the placement isunaltered.

A computer implemented method is also provided for determining a cleanupline routing for a bus line or control line of an integrated circuit,the method comprising:

taking a finalized relative placement of components of the integratedcircuit, the placement including routing constraints and port locations;

taking an initial routing for each bus line or control line; and

determining a cleanup line routing for each bus line or control linebased on the placement and the initial routing, the cleanup line routingconnecting the initial routing for each bus line or control line toports associated with each bus line or control line.

An article of manufacture comprising a computer readable medium bearinga program code embodied therein for performing the above method and anintegrated circuit design tool comprising: a processor; and memorycoupled to the processor including instructions which when executed bythe processor perform the above methods are also provided by the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow diagram for a method of taking a netlist andforming a relative placement of the components of the circuit.

FIG. 2A illustrates a netlist including representations of components ofa circuit.

FIG. 2B illustrates a bus line group based on the netlist shown in FIG.2A.

FIG. 2C illustrates a control line group based on the netlist shown inFIG. 2A.

FIG. 2D illustrates a structural similarity group based on the netlistshown in FIG. 2A.

FIG. 3 illustrates an example of a process flow for forming structuregroups from a netlist.

FIG. 4 illustrates an embodiment of a flow diagram for performing aninitial placement according to the present invention.

FIG. 5A illustrates a bus/control line positioning template formed basedon the bus line order specified in the netlist.

FIG. 5B illustrates the placement of the AD group of components from thestructural similarity group in bus line tracks B0 and B1.

FIG. 5C illustrates the placement of additional groups of componentsfrom the structural similarity group to the bus line tracks.

FIG. 5D illustrates the placement of the remaining components from thestructural similarity group to the bus line tracks.

FIG. 5E illustrates the result of performing a minimum cut algorithmupon the initial placement of the components of FIG. 5D.

FIG. 5F represents an 8-bit adder circuit representation after havingthe circuit design optimized according to a method of a presentinvention.

FIG. 6A illustrates an initial relative placement of components andtheir connectivities.

FIG. 6B illustrates the performance of a minimum cut algorithm on theinitial relative placement of components illustrated in FIG. 6A.

FIG. 6C illustrates the repositioning of the components after completionof the minimum cut algorithm.

FIG. 7A illustrates the analysis of boundary conditions for a firstcell.

FIG. 7B illustrates the manipulation of a component.

FIG. 7C illustrates a layout before the diffusion boundary method isemployed on a layout.

FIG. 7D illustrates a layout after the diffusion boundary method isemployed on a layout.

FIG. 8A shows a flow process diagram of one embodiment of a method fordetermining a bus line routing for components of an integrated circuit.

FIG. 8B shows a flow process diagram of one embodiment of a method fordetermining a routing order based on at least one criterion.

FIG. 8C shows a flow process diagram of one embodiment of a method fordetermining an initial routing for each bus line based on the routingconstraints and the port locations.

FIG. 8D shows a flow process diagram of one embodiment of a method fordetermining a cleanup routing for each port location based on theinitial routing, the routing constraints, and the port locations.

FIGS. 8E-8L show one example of a method for determining a bus linerouting for components of an integrated circuit.

FIG. 9A shows a flow process diagram of one embodiment of a method fordetermining a control line routing for components of an integratedcircuit.

FIG. 9B shows a flow process diagram of one embodiment of a method fordetermining an initial routing for each control line based on therouting constraints and the port locations.

FIG. 9C shows a flow process diagram of one embodiment of a method fordetermining a cleanup routing for each port location based on theinitial routing, the routing constraints, and the port locations.

FIGS. 9D-9K show one example of a method for determining a control linerouting for components of an integrated circuit.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a series of methods employable in theoverall process of taking a netlist representation of components of anintegrated circuit and designing an integrated circuit layout includinga placement scheme for the components forming the circuit and a routingscheme for the circuit. These different methods may be employed alone orin combination with other methods of the present invention.

One of the methods provided by the present invention is for forming astructure group from a netlist of components of an integrated circuit,the structure group being useful for later performing a relativeplacement of the components forming the circuit. In one embodiment, themethod comprises: taking a netlist representation of components of anintegrated circuit; forming groups of the components included in thenetlist representation which have at least a selected degree ofstructural similarity between each other; and forming a structuralsimilarity group which includes those groups of components identified ashaving at least the selected degree of structural similarity. Thisstructure group is used in the method for performing a relativeplacement of the components.

An article of manufacture comprising a computer readable medium bearinga program code embodied therein for performing the above method and anintegrated circuit design tool comprising: a processor; and memorycoupled to the processor including instructions which when executed bythe processor perform the above methods are also provided by the presentinvention.

As used herein, structural similarity includes similarities betweendifferent components based on which bus lines and control lines eachcomponent is connected to in the circuit. Other structural features mayalso be used in determining a degree of structural similarity includingbuses, controls, nets, component types, power requirements, cellequivalents, and the like. The degree of structural similarity may referto a ratio between the number of structural features which twocomponents have in common and the total number of structural featuresused to evaluate structural similarity. Typically, the component withthe most structural features is placed in the denominator and the numberof structural features which that component shares with a secondcomponent is placed in the numerator of the ratio. Alternatively, adegree of similarity may refer to a number of structural features whichtwo components have in common. The term “selected degree” refers to thedegree of structural similarity required to be included in the list. Itis noted that the degree of structural similarity may be selected by theuser. Hence, a user may select between different degrees of structuralsimilarity (e.g., at least 10%, 20%, 25%, 33%, 50%, 66%, 75%, 80%, or100% structural similarity).

The groups of structurally similar components formed may be required tohave a minimum number of components, e.g., 2, 3, 4 or more. Also, alimit may be set for the maximum number of components that can beincluded in a group. This maximum number may correspond to a maximum busline width for the integrated circuit being laid out.

Another method provided is for forming a relative placement ofcomponents of an integrated circuit from a netlist using a structuregroup. FIG. 1 illustrates a flow diagram for one embodiment of themethod. As illustrated in the figure, the method comprises: taking anetlist representation of components of an integrated circuit; forminggroups of components within the netlist which have at least a selecteddegree of structural similarity between each other; making a structuralsimilarity group which includes those groups of components identified ashaving at least the selected degree of structural similarity; performingan initial relative placement of the groups of components; modifying therelative placement of components relative to control lines such thatwire lengths between components are minimized; and adding to therelative placement those components from the netlist which were notincluded in the groups of components.

An article of manufacture comprising a computer readable medium bearinga program code embodied therein for performing the above method and anintegrated circuit design tool comprising: a processor; and memorycoupled to the processor including instructions which when executed bythe processor perform the above method is also provided by the presentinvention.

An important aspect of this method is the concept of taking a group ofcomponents included in a netlist and forming a subgroup of componentscorresponding to those components which have a selected degree ofstructural similarity with at least one other component in the circuit.Components of the circuit which do not satisfy the selected degree ofsimilarity requirement are not used while an initial relative placementof the grouped components is performed, thereby reducing the complexityof that placement. The components that are set aside during this initialrelative placement due to lack of sufficient structural similarity maybe readily placed after the initial relative placement.

A relative order for bus lines in the circuit is generally specified bythe circuit designer and can be found in the netlist. According to avariation of the above method, the relative order for the bus linesspecified in the netlist is preserved throughout the relative placement.Accordingly, the step of performing an initial relative placement of thegroups of components includes placing the groups of components such thatthe relative order for the bus lines specified in the netlist ispreserved. The step of reducing wire lengths between components ofinitial relative placement is performed with regard to the controllines. The order of the bus lines is preserved during this process.

By preserving the order of the bus lines specified in the netlist duringthe process, integrated circuits can be designed where the different buslines in the circuit are substantially straight and have substantiallythe same length. Also, by preserving the order of the bus lines, thetiming of signals reaching components on different bus lines whichperform the same functions can be made to be substantially the samebecause the length of each bus line is the same length. Havingsubstantially the same timing on different bus lines enables there to berelatively zero displacement between the timing of an operation on afirst bus line and an operation on a second, different bus line incircuits designed according to the present invention. Use of the processalso enables integrated circuits to be designed where the length of thebus lines in the circuit is minimized. This enables the resultingintegrated circuit to have improved processing speed and eliminates theneed for deconvolution.

Further according to the above method, relative placements may beperformed such that a relative placement of a group of structurallysimilar components is performed. Then, whenever a group of the samecomponents is identified, the relative placement that had beendetermined for that group of components is utilized, thereby reducingthe need to perform multiple redundant relative placements and improvingthe rate at which a relative placement of an entire circuit can beperformed.

Further according to the above method, the step of adding to therelative placement those components from the netlist which were notincluded in the groups of components is preferably performed iterativelywhere each component is placed such that cut and wire lengths betweencomponents are minimized.

Another method provided is for modifying a relative placement ofcomponents of an integrated circuit based on an analysis of adjacentcomponents for shared resources. One embodiment of this methodcomprises: taking a relative placement of components of an integratedcircuit; analyzing adjacent components for resources associated with thecomponents which can be shared; and modifying the relative placement ofcomponents such that adjacent components share identified sharableresources. An integrated circuit design tool comprising: a processor;and logic for performing the above method is also provided by thepresent invention.

Another method that is provided is for determining at least part of abus line routing for each bus line of an integrated circuit, each busline routing including an initial routing and a cleanup routing. Oneembodiment of the method includes taking a finalized relative placementof components of the integrated circuit, the placement including routingconstraints and at least a first and second port locations associatedwith each bus line; determining a routing order for the bus lines basedon at least one criterion; and determining an initial routing for eachbus line based on the placement, each initial routing beingsubstantially straight and substantially parallel to a bus line axis, alength of each initial routing based on a distance along the bus lineaxis between the first and second port locations, a position of eachinitial routing based on an average distance orthogonal to the bus lineaxis between at least the first and second port locations, wherein theplacement is unaltered.

An article of manufacture comprising a computer readable medium bearinga program code embodied therein for performing the above method and anintegrated circuit design tool comprising: a processor; and memorycoupled to the processor including instructions which when executed bythe processor perform the above method is also provided by the presentinvention.

Another method that is provided is for determining at least a part of acontrol line routing for each control line of an integrated circuit,each control line routing including an initial routing and a cleanuprouting. One embodiment of the method includes taking a finalizedrelative placement of components of the integrated circuit, theplacement including routing constraints and at least a first and secondport locations associated with each control line; and determining aninitial routing for each control line based on the placement, eachinitial routing being substantially straight and substantially parallelto a control line axis, a length of each initial routing based on adistance along the control line axis between the first and second portlocations, a position of each initial routing based on an averagedistance orthogonal to the control line axis between at least the firstand second port locations, wherein the placement is unaltered.

An article of manufacture comprising a computer readable medium bearinga program code embodied therein for performing the above method and anintegrated circuit design tool comprising: a processor; and memorycoupled to the processor including instructions which when executed bythe processor perform the above method is also provided by the presentinvention.

Another method that is provided is for determining a cleanup linerouting for a bus line or control line of an integrated circuit. Oneembodiment of the method includes taking a finalized relative placementof components of the integrated circuit, the placement including routingconstraints and port locations; taking an initial routing for each busline or control line; and determining a cleanup line routing for eachbus line or control line based on the placement and the initial routing,the cleanup line routing connecting the initial routing for each busline or control line to ports associated with each bus line or controlline.

An article of manufacture comprising a computer readable medium bearinga program code embodied therein for performing the above method and anintegrated circuit design tool comprising: a processor; and memorycoupled to the processor including instructions which when executed bythe processor perform the above method is also provided by the presentinvention.

An important aspect of this method is that routings between componentsare created by connecting each component to an adjacent bus line orcontrol line, as opposed to creating routings directly betweencomponents. By utilizing bus lines and control lines to route betweencomponents, the total route length between different components isreduced.

Each of the above methods will now be described in greater detail below.

1. Method for Forming a Structural Similarity Group From A Netlist forUse In Performing a Relative Placement of Components of an IntegratedCircuit

A netlist refers to list of representations of components forming all orpart of an integrated circuit. The representations may include a varietyof symbolic representations which are used to describe the components ofthe circuit. These symbolic representations typically include anidentification of the type of component and their interconnections, forexample, symbolic representations of the bus line and control lineconnections for each component. Examples of additional symbolicrepresentations that may be included in a netlist representationinclude, but are not limited to regular nets, component types, andconnectivities.

FIG. 2A illustrates a netlist including representations of components ofa circuit. As illustrated, the netlist provides a list of components(and=and gates; nor=nor gates; mux=multiplexers; and inv=inverters). Foreach component, a list is provided of the bus lines (ina, inb, inab,inbb, na, ncmp) and control lines (vdd, eualb, nnn, ni, nx, ny) to whichthe component is connected. The netlist also provides an initial orderfor the bus lines (ina, inb, inab, inbb, na, ncmp).

According to one method of the present invention, a netlist, such as theone illustrated in FIG. 2A, is analyzed for the presence of differentstructural requirements in order to form structure groups which arelater used to perform a relative placement of the components listed inthe netlist. Each structure group includes representations of how thenetlist representations satisfy the structural requirement used to formthe structure group.

A variety of different structural requirements may be used to form thestructure groups. Examples of different structural requirements that maybe used include, but are not limited to, whether a component isconnected to a particular bus line or group of bus lines, whether acomponent is connected to a particular control line or group of controllines, and whether there is a degree of structural similarity betweentwo or more components regarding their connectivity to different buslines, control lines and other components.

FIG. 2B illustrates a bus line group based on the netlist shown in FIG.2A. As illustrated, the bus line group lists the different bus lines inthe initial order provided in the netlist.

FIG. 2C illustrates a control line group based on the netlist shown inFIG. 2A.

As described above, structural similarity refers to similarities betweendifferent components based on which bus lines and control lines eachcomponent is connected to in the circuit. Other structural features mayalso be used in determining a degree of structural similarity includingbuses, controls, nets, component types, and connectivities to otherstructures. A degree of similarity generally refers to a ratio betweenthe number of structural features which two components share in commonand the total number of structural features used to evaluate structuralsimilarity. Alternatively, a degree of similarity may refer to a numberof structural features which two components have in common. Optionally,certain forms of structural similarity, such as common bus line orcontrol line connectivity, may be given greater significance than otherforms of structural similarity.

The degree of structural similarity required to satisfy the list may beselectable by the user. For example, a user may select between differentdegrees of structural similarity (e.g., at least 10%, 20%, 25%, 33%,50%, 66%, 75%, 80%, or 100% structural similarity).

FIG. 2D illustrates a structural similarity group based on the netlistshown in FIG. 2A where it is required that components have at least 100%structural similarity. In forming the structural similarity group, itwas required that the components appear in both the bus line and controlline constraint lists.

As will be explained herein in greater detail, the structural similarityconstraint list is used to divide the netlist into a first group ofcomponents which have a specified degree of structural similarity withat least one or more other components, and a second group of componentswhich do not have the specified degree of structural similarity with asufficient number of other components in the netlist. The first groupwhich satisfy the structural similarity requirements are used to performan initial relative placement of components. During this initialrelative placement, the second group which lack sufficient structuralsimilarity to be included in the group are not placed. By dividing thecomponents in the netlist into this first and second group ofcomponents, the complexity of creating an initial relative placement isreduced. Also, the formation of these two groups insures that componentswith the highest degree of structural similarity are given priority whendetermining a relative placement.

While the above method is described with regard to creating a singlestructural similarity group, it is noted that it may be desirable toform a group with a high degree of structural similarity, and one ormore other groups which have a lower degree of structural similarity.This allows one to have multiple levels of prioritization in creating arelative placement of components.

FIG. 3 illustrates an example of a process flow for forming structuregroups from a netlist. As illustrated, the process includes the step oftaking a netlist and building a data structure which includescomponents, bus lines, and control lines. The data structure mayoptionally further include additional information about the circuit andits components.

A group of structure lines is generated for each bus line based on thosecomponents on the same bus line.

A group of structure lines is also generated for each control line basedon those components on the same control line. For each control line, amaximum control line component length may be specified. As structurelines are generated, control lines having a length equal to or shorterthan the control line component maximum length may be allowed to beformed. Those structure lines having a length greater than the controlline component maximum length may be discarded.

A group of structure lines based on structural similarity may also beformed. In this flow, different bits of the same bus are considered tobe the same connection.

2. Method for Forming a Relative Placement of Components of anIntegrated Circuit Using a Structural Similarity Group

Another method provided is for forming a relative placement ofcomponents of an integrated circuit from a netlist using a structuralsimilarity group. As described in Section 1, one or more structuregroups may be formed from a netlist. This method may be applied to allor a portion of an integrated circuit. The method can also be used toenhance the placement of components of an integrated circuit, regardlessof the circuit's origin, as long as structure groups are provided asdescribed above.

In one embodiment, the method comprises: taking a netlist representationof components of an integrated circuit; forming groups of componentswithin the netlist which have at least a selected degree of structuralsimilarity between each other; making a structural similarity groupcomprising those groups of components identified as having at least theselected degree of structural similarity; performing an initial relativeplacement of the groups of components; modifying the relative placementof components relative to control lines such that wire lengths betweencomponents are minimized; and adding to the relative placement thosecomponents from the netlist which were not included in the groups ofcomponents.

In general, a netlist includes representations for N components whichcorrespond to all or part of an integrated circuit. The structuralsimilarity group formed in Section 1 above includes M components,wherein M<N. Those components from the netlist which are not included inthe structural similarity group lo are N−M in number. The relativeplacement method described in this section allows for the relativeplacement of N components to be performed in at least two stages where Mcomponents (those components from the netlist which appear in thestructural similarity group) are placed and then N−M components areplaced (those components from the netlist which do not appear in thestructural similarity group).

An important aspect of this method is the concept of taking a group ofcomponents included in a netlist and forming a subgroup of componentscorresponding to those components which have a selected degree ofstructural similarity with at least one other component in the circuit.Components of the circuit which do not satisfy the selected degree ofsimilarity requirement are not used while an initial relative placementof the grouped components is performed, thereby reducing the complexityof that placement. The components that are set aside during this initialrelative placement due to lack of sufficient structural similarity maybe readily placed after the initial relative placement.

A relative order for bus lines in the circuit is generally specified bythe circuit designer and can be found in the netlist. According to avariation of the above method, the relative order for the bus linesspecified in the netlist is preserved throughout the relative placement.Accordingly, the step of performing an initial relative placement of thegroups of components includes placing the groups of components such thatthe relative order for the bus lines specified in the netlist ispreserved. The step of reducing wire lengths between components ofinitial relative placement is performed with regard to the controllines. The order of the bus lines is preserved during this process.

By preserving the order of the bus lines specified in the netlist duringthe process, integrated circuits can be designed where the different buslines in the circuit are substantially straight and have substantiallythe same length. Also, by preserving the order of the bus lines, thetiming on different bus lines is substantially the same, because thelength of each bus line is substantially the same. Having substantiallythe same timing on different bus lines enables there to be relativelyzero displacement between the timing of an operation on a first bus lineand an operation on a second, different bus line in circuits designedaccording to the present invention. Use of the process also enablesintegrated circuits to be designed where the length of the bus lines inthe circuit is minimized. This enables the resulting integrated circuitto have improved processing speed and eliminates the need fordeconvolution.

Furthermore, according to the above method, the step of adding to therelative placement those components from the netlist which were notincluded in the groups of components is preferably performed iterativelywhere each component is placed such that cut and wire lengths betweencomponents are minimized.

The above method will now be described in more detail with references toFIGS. 4, 5A-5F, and 6A-6C.

FIG. 4 illustrates a flow diagram of the method for performing arelative placement of components using a structure group. This methodmay be incorporated into a software program and run on a processor (notshown) in order to determine a relative placement. In step 410, datafrom the structural similarity group is taken and in step 420, the datais used to perform an initial relative placement (See FIG. 1).

FIGS. 5A-5F illustrate an embodiment of an initial relative placementstep. As illustrated in FIG. 5A, a bus/control line positioning templateis formed based on the bus line order specified in the netlist. Thebus/control positioning template is used as a backdrop for placing thecomponents in positions relative to each other and in the vicinity ofwhere the bus and control lines will be ultimately placed. After all ofthe components have been placed, bus and control lines are actuallypositioned (See Sections 4 and 5).

As described above, a relative order for bus lines in the circuit isgenerally specified by the circuit designer and can be found in thenetlist. This relative order of bus lines is preferably conserved in thebus/control positioning template. It should be noted that in thisrepresentation that only a few control lines are illustrated but in anactual application the number of buses and control lines can range fromseveral to hundreds of thousands.

As illustrated in FIG. 5A, reference numerals B0-B6 are positioned alongthe x-axis and identify the zero bit through second bit bus line regionswherein the zero bit through second bit bus lines will be ultimatelypositioned. The reader should note that in FIGS. 5A-5F the finalplacement of the bus lines will be parallel to the y-axis, i.e. the buslines run from top to bottom in this illustration. Along the x-axis thereference numerals C0-C2 represent the zero through second control lineregions of a portion of the bus/control line positioning template. Asillustrated in FIG. 5B, the AD group of components from the structuralsimilarity group introduced in FIG. 1 is placed in bus line tracks B0and B1 to which the component group was associated in the netlist. Asillustrated in FIGS. 5C and 5D, this process is repeated until all ofthe groups of components are included in the initial relative placement.

Further according to the above method, relative placements may beperformed such that a relative placement of a group of structurallysimilar components is performed. Then, whenever a group of the samecomponents is identified, the relative placement that had beendetermined for that group of components is utilized, thereby reducingthe need to perform multiple redundant relative placements and improvingthe rate at which a relative placement of an entire circuit can beperformed.

For example, FIG. 5F represents an 8-bit adder circuit representationafter having the circuit design optimized according to a method of thepresent invention. As additional 8-bit adder circuits are identifiedwithin the circuit, the already determined structure for an 8-bit addercircuit can be utilized again and again. As a result, the structure ofcomponent groups, such as an 8-bit adder circuit, can be determined onceand used over and over again. Of course the additional 8-bit addercircuits may have different control and bus lines, but these differencesare taken care of in the netlist.

By employing duplication of the structures and their placement, thepresent invention promotes uniformity in IC design, thereby enablingstructures to have substantially the same timing on different bits ofthe same bus, minimization of the length of the bus lines in thecircuit, and improved processing speed. In addition, the processing timerequired to design the circuit is significantly reduced.

Referring back to FIG. 4, one of many conventional algorithms may beperformed in step 430 to reduce wire lengths between components ofinitial relative placement. For example, minimum cut algorithm may beused to analyze the placement of the components to minimize the numberof line cuts and wire length of the bus line such that both areminimized.

FIGS. 6A-6C illustrate the performance of minimum cut algorithm. FIG. 6Aillustrates an initial relative placement of components and theirconnectivities. As illustrated in FIG. 6B, the minimum cut algorithmmanipulates the positioning of each of the components placed, while notviolating the bus track or the control lines placements associated withthe particular component as indicated by the data provided in thenetlist. FIG. 6C depicts the repositioning of the components aftercompletion of the minimum cut algorithm in accordance with step 430 ofthe process flow shown in FIG. 4.

The result of performing the minimum cut algorithm upon the initialplacement of the components of FIG. 5D is illustrated in FIG. 5E. Asshown in FIG. 5E, the SQR and TMN groupings were unaffected by theminimum cut algorithm and their initial relative placement was notmodified. With respect to the AD, GJL, HW, PE groupings the minimum cutalgorithm reassigned the groupings and modified the relational order orthe relational position or both in the bus/control line positioningtemplate.

As illustrated in FIGS. 5A-5E and 6A-6C, the process of placingcomponents from the structural similarity group may be performed whereall components are positioned at once and then subjected to a processwhere the number of line cuts and wire lengths are minimized.

Referring once again to FIG. 4, step 440 relates to the placement ofthose components from the netlist which do not appear in the structuralsimilarity group and hence are not positioned during steps 410-430. Inthis step, those components not appearing in the structural similaritygroup are added to the placement according to their connectivities tothe components that have already been placed. The placement of thesecomponents may be performed by a variety of different methodologiesdesigned to minimize the number of line cuts and wire lengths generatedby a particular placement.

The initial placement method described in regard to steps 410-440 ofFIG. 4 enables all or a portion of an integrated circuit to be designedwhich has substantially the same timing on different bus lines andprovides for relatively zero displacement, i.e. “skew”, between thetiming of an operation on a first bus line and an operation of a seconddifferent bus line in circuits designed according to the presentinvention. Use of this process also enables integrated circuits to bedesigned where the length of the bus lines and the number of line cutsare minimized. Thus enabling the resulting integrated circuit to haveimproved processing speed and the elimination for the need ofdeconvolution.

3. Method for Modifying a Relative Placement of Components of anIntegrated Circuit by Analyzing Adjacent Components for Shared Resources

A method is provided for modifying a relative placement of components ofan integrated circuit based on an analysis of adjacent components forshared resources. One embodiment of this method includes: taking arelative placement of components of an integrated circuit; analyzingadjacent components for resources associated with the components whichcan be shared; and modifying the relative placement of components suchthat adjacent components share identified sharable resources.

The basic premise of the above described method is that there arecertain resources or commonalities between adjacent components that canbe shared by the adjacent components (cells). Therefore, by identifyingthose shareable resources in adjacent cells, it is possible to reorientthe adjacent cells relative to each other such that the common resourcescan be overlapped and shared. One of the more common resources to beshared is the power bus, but pin/port locations may also be shared, thusrequiring less port connections. It should be noted that signal orcontrol lines or any common structure may also be shared.

The above described method provides for enhanced integrated circuitdesign and can be employed independently of or in combination with oneor more methods of the present invention. It is noted that this methodmay be incorporated into a software program and run on a processor (notshown) in order to perform the method.

The step of analyzing adjacent cells for resources associated with thecells, which can be shared, can include an analysis of the boundaryconditions of each component. The component (cell) is divided into tworegions for analysis purposes. The central region is identified as thecentral area of the component, wherein the circuit design information issymbolically associated. For instance, the first region may represent anadder, inverter, transistor, or similar device. The component is thenfurther divided into a boundary region, which is the region along theedge of the component not including the central region. The boundaryregion is the area of each component that is analyzed to determine ifresource sharing is available among adjacent components.

Each component has either two power buses or two signal buses or onepower bus and one signal bus connected to it. If the component has onepower and one signal bus the side nearest the power or signal bus iscalled the power or signal bus side, respectively. If the boundaryconditions of the next adjacent component has the same power bus orother shareable structure then the method attempts to commonly employthat structure. For illustration purposes used herein, it will beassumed that the power bus is the common structure.

The step of modifying the relative placement of components such thatadjacent components share identified sharable resources includes, but isnot limited to, manipulating, i.e. rotating, inverting, and/or flippingadjacent components in order to determine whether the power bus sides ofthe components can be aligned to take advantage of the power buscommonality that they share. Two or more components may share multiplestructures, such as a common power and signal bus.

In addition to evaluating whether power bus lines can be shared, themethod includes manipulating each component in order to analyze theboundary conditions of each component and identifying structures withinthe component which can be shared with other adjacent components. Acomponent can conceivably share resources with multiple adjacentcomponents and therefore may be analyzed multiple times before a finalconfiguration is determined, thereby optimizing the resources of as manyof the components adjacent to the component under scrutiny.

The method also includes a step of fine positioning individualcomponents to allow for the elimination of multiple port-to-bus andcontrol-to-bus junctions by aligning the components such that one portto bus or port to control junction will service at least two components.This process is repeated on the component being analyzed to optimize theport connections among the components adjacent to the component beinganalyzed.

Performance of the above described method will now be described indetail with references to FIGS. 7A-7D. In FIG. 7A, a first component 700boundary condition is analyzed. Analysis reveals that the firstcomponent 700 contains a power bus 710 and two port to bus junctions 720and 725 connected to power bus 710. Also according to the method, onecontrol bus 730 and one port to control junction 735 connected tocontrol line 730 are identified, as show in FIG. 7A. The boundaryconditions are then analyzed and power bus 740 and bus to port junctions750 and 755, control bus 760 and port to control junction 765 areidentified. According to the method, it is then determined that thepower bus 710 and 740 are the same and that control buses 730 and 760are the same.

The placement of the components is then manipulated such that thecommonalities are shared as depicted in FIG. 7B. In FIG. 7B, component700 and component 770 are overlapped such that they share common buslines and control lines as well as port connections. In a conventionalprocess, the power buses 710 and 740 as well as control buses 730 and760 would have both been created in the manufacturing process, therebyutilizing twice as much chip area as necessary to provide the samefunctionality.

According to the method, the diffusion sharing boundary analysis iscontinued until each component has been analyzed and manipulated topromote sharing of any commonalities. Once each component has beenanalyzed, an overlapped final placement file is generated.

FIGS. 7C and 7D illustrate a circuit layout before and after thediffusion boundary method is employed on the layout. The over-lappedregion depicted in FIG. 7D represents the shared regions and it isreadily apparent from this figure the potential chip area savings whenthis process is applied to hundreds of thousands of components.

By taking into consideration the identified commonalities the presentinvention exploits this knowledge to create higher densities in an ICdesign, decreased hot spots, decreased cross talk, faster through puttime, lower cost and speed to market. With respect to the higherdensities, the improvement can be up to 30% or higher depending on thedesign constraints and the type of IC that is being designed.

4. Method for Determining Bus Line Routing for Components of anIntegrated Circuit

Instead of routing bus lines from port to port, analogous to buildingindividual roads from “house” to “house”, the method of the presentinvention first determines an initial routing, analogous to first pavinga major “street”, then determines a cleanup routing from the initialrouting to each port, analogous to paving individual “driveways” leadingfrom the major “street” to each “house”. This method simplifies therouting task. More importantly, this method is capable of generatingcircuit layouts which minimize skew or timing differences by minimizingthe length differences between the complete bus lines of different bits.

FIG. 8A shows a flow process diagram of one embodiment of a method fordetermining a bus line routing for components of an integrated circuit.The bus line routing includes an initial routing and a cleanup routing.The method includes: (1) receiving routing constraints and portlocations associated with each bus line (block 810); (2) determining arouting order (block 820); (3) determining an initial routing for eachbus line based on the routing constraints and the port locations, eachinitial routing being substantially straight (block 830); and (4)determining a cleanup routing for each bus line based on the initialrouting, the routing constraints, and the port locations, the cleanuprouting connecting the initial routing for each bus line to portsassociated with each bus line (block 840).

1. Receiving Routing Constraints and Port Locations

Receiving routing constraints and port locations associated with eachbus line (block 810) includes receiving any information necessary toperform routing of the bus lines. Routing constraints may includephotolithography limitations and other information such as bus linewidths, bus line spacing, and bus line shielding requirements. Portlocations may include coordinates for each port and the bus line towhich it must be connected. Port locations may be given with referenceto two orthogonal axes, such as Cartesian coordinates. These axes may bedefined as a bus line axis and an orthogonal axis, where each initialrouting may be substantially parallel to the bus line axis. Routingconstraints and port locations may be taken from a component placementgenerated using the methods described in previous sections, or acomponent placement generated from any auto-place and -route tool.

2. Determining a Routing Order

FIG. 8B shows a flow process diagram of one embodiment of a method fordetermining a routing order based on at least one criterion (block 820).This method may include: (1) assigning a score structure to eachcriterion based on an importance of each criterion (block 822); (2)assigning scores to each bus line based on the score structure for eachcriterion (block 824); (3) determining a total score for each bus line(block 826); and (4) determining a routing order based on the totalscores (block 828).

The criteria may include bus line function, bus line width, anduser-defined criteria. Bus line function may include whether a bus lineis an input/output bus lines, which is a bus line connected to theoutside world, versus an internal bus line, which is a bus lineconnected within a cell. Bus line width is a function of the number ofports connected to the bus lines. User-defined criteria may involveconsiderations of timing issues.

Assigning a score structure to each criterion based on an importance ofeach criterion (block 822) may be predetermined or set by the user. Forexample, bus line function may be given greatest importance, followed bybus line width and user-defined criteria. Within each criteria,different features are assigned different scores on the score structure.For example, input/output bus lines may be given priority over internalbus lines, and wider bus lines may be given priority over narrower buslines.

Assigning scores to each bus line based on the score structure for eachcriterion (block 824) may include looking at each bus lines anddetermining what score each bus line should receive for each of thecriteria. Determining a total score for each bus line (block 826) anddetermining a routing order based on the total scores (block 828) mayinclude adding up the scores to obtain a total score for each bus lineand ordering the bus lines according to the total score each bus linehas received.

For example, a weighting system may be used to assign a number ofpriority points to each criterion, which are then added up afterconsideration of each criterion to give a total priority score.

EXAMPLE 1

A routing order for three bus lines A, B, and C must be determinedaccording to two criteria, in order of importance: (1) bus linefunction; and (2) bus line width. Bus line function is given a scoreranging from 0-3, where 0 is an internal bus line and 3 is aninput/output bus line. Bus line width is given a sore ranging from 1-3,from narrowest to widest bus line. The bus line with the greatest scoreis routed first, and so on. Bus line A is an internal bus line and thewidest bus line. Bus line B is an input/output bus line and thenarrowest bus line. Bus line C is an internal bus line and the secondwidest bus line.

Bus line Bus line f(x) Bus line width Total score Routing order A 0 3 32 B 3 1 4 1 C 0 2 2 3

Thus, bus line B will be routed first, followed by bus line A and busline C. Note that the score structure has the effect of giving bus linefunction greater importance than bus line width.

3. Determining an Initial Routing

FIG. 8C shows a flow process diagram of one embodiment of a method fordetermining an initial routing for each bus line based on the routingconstraints and the port locations, each initial routing beingsubstantially straight (block 830). The method may include: (1)determining a length for each initial routing based on a distance alongthe bus line axis between a first and second port locations (block 832);and (2) determining a position for each initial routing based on anaverage distance orthogonal to the bus line axis between at least thefirst and second port locations (block 834). The method may furthercomprise: (3) determining an alternate position for each initial routingwhere a blockage is present (block 836).

Each of the port locations may be associated with a first coordinatealong the bus line axis and a second coordinate orthogonal to the busline axis. Determining a length for each initial routing (block 832) mayinclude calculating a difference of the first coordinates associatedwith the first and second port locations. Determining a position foreach initial routing (block 834) may include calculating an average ofthe second coordinates associated with at least the first and secondport locations.

If Cartesian coordinates are used, determining a length for each initialrouting (block 832) may include calculating a difference of the xcoordinates associated with the first and second bus line portlocations. Determining a position for each initial routing (block 834)may include calculating an average of the y coordinates associated withthe first and second port locations and possibly other port locations.

Blockages may arise where the space or track needed for the initialrouting has already been used, such as for a previous routing.Determining an alternate position for each initial routing where ablockage is present (block 836) may include defining a search regionbased on at least the first and second port locations, and thenselecting a closest available position located within the search region.The search region may be a rectangular routing window which has at leasttwo comers defined by the first and second port locations. For example,the routing window may have diagonally opposing corners defined by thefirst and second port locations. The alternate position may be selectedby first looking to tracks immediately adjacent to the average position.

4. Determining a Cleanup Routing

FIG. 8D shows a flow process diagram of one embodiment of a method fordetermining a cleanup routing for each port location based on theinitial routing, the routing constraints, and the port locations, thecleanup routing connecting the initial routing for each bus line toports associated with each bus line (block 840). The method may include:(1) determining a length for each cleanup routing based on a distancebetween the initial routing and the port location (block 842); and (2)determining a position for each cleanup routing based on the initialrouting and the port location (block 844). The method may furthercomprise: (3) determining an alternate position for each cleanup routingwhere a blockage is present (block 846). An external router normallyused as part of an auto-place and -route tool may be used to performcleanup routing.

Determining a length for each cleanup routing based on a distancebetween the initial routing and the port location (block 842) mayinclude finding the shortest distance between the initial routing andeach port. Determining a position for each cleanup routing based on theinitial routing and the port location (block 844) may includepositioning the cleanup routing to connect the initial routing and eachport.

Blockages may arise where the space or track has already been used, suchas for a previous routing. Determining an alternate routing for eachcleanup routing where a blockage is present (block 846) may includegenerating a cleanup routing around the blockage. The alternate routingmay be selected by first looking to tracks immediately adjacent to theshortest routing, and then determining the shortest Manhattan lengthfrom the initial routing to each port.

EXAMPLE 2

FIGS. 8E-8L show one example of a method for determining a bus linerouting for components of an integrated circuit. FIG. 8E shows aplacement of components 850 of an integrated circuit. The placementincludes information about the individual placement of each component850. Components 850 may be of different sizes, abut or overlap eachother, and/or be spaced at varying distances from each other. Components850 may each have one or more ports 852 to be connected to the bus line.The routing constraints and port locations may be part of the placementinformation, or separate.

A routing order for the bus lines is determined according to bus linefunction and bus line width. Bus line routing is determined in therouting order.

FIG. 8F shows an initial routing 860 for the bus line. Initial routing860 is substantially straight, and parallel to a bus line axis, which iscoincident to the y-axis as shown in the figures. The length of initialrouting 860 is determined along the bus line axis, based on thelocations of the two furthest ports 852 for this particular section ofthe bus line. The position of initial routing 860 is determined along anaxis orthogonal to bus axis, which is coincident to the x-axis as shownin the figures. The position of initial routing 860 is determined bycalculating an average of the x-values of the locations of ports 852.This approach minimizes the length of the cleanup routing.

FIG. 8G shows a blockage 856 present and interfering with initialrouting 860. A search region 858 is then created, in this case arectangular region which uses ports 852 to define its comers. FIG. 8Hshows an alternate position for initial routing 860 selected to avoidinterference with blockage 856. Initial routing 860 is moved by lookingto the tracks immediately adjacent to blockage 856. For example, thetracks immediately to the top and the bottom of blockage 856 may besearched and their availability determined. Initial routing 860 may bemoved to still minimize the lengths of the cleanup routing in view ofblockage 856.

FIG. 8I shows initial routing 860 complete and ready for cleanuprouting. FIG. 8J shows cleanup routing 870 which connects initialrouting 860 to each of ports 852. In general, cleanup routing 870 isselected to be the shortest distance from initial routing 860 to each ofports 852. A blockage 856 interferes with one section of cleanup routing870. FIG. 8K shows an alternate routing for this section of cleanuprouting 870 to circumvent blockage 856. FIG. 8L shows both initialrouting 860 and cleanup routing 870 complete.

5. Method for Determining Control Line Routing for Components of anIntegrated Circuit

Instead of routing control lines from port to port, analogous tobuilding individual roads from “house” to “house”, the method of thepresent invention first determines an initial routing, analogous tofirst paving a major “street”, then determines a cleanup routing fromthe initial routing to each port, analogous to paving individual“driveways” leading from the major “street” to each “house”. This methodsimplifies the routing task. More importantly, this method is capable ofgenerating circuit layouts which minimize skew and timing differences byminimizing the lengths of the control lines.

FIG. 9A shows a flow process diagram of one embodiment of a method fordetermining a control line routing for components of an integratedcircuit. The control line routing includes an initial routing and acleanup routing. The method includes: (1) receiving routing constraintsand port locations associated with each control line (block 910); (2)determining an initial routing for each control line based on therouting constraints and the port locations, each initial routing beingsubstantially straight (block 920); and (3) determining a cleanuprouting for each control line based on the initial routing, the routingconstraints, and the port locations, the cleanup routing connecting theinitial routing for each control line to ports associated with eachcontrol line (block 930).

1. Receiving Routing Constraints and Port Locations

Receiving routing constraints and port locations associated with eachcontrol line (block 910) includes receiving any information necessary toperform routing of the control lines. Routing constraints may includephotolithography limitations and other information such as control linewidths, control line spacing, and control line shielding requirements.Port locations may include coordinates for each port and the controlline to which it must be connected. Port locations may be given withreference to two orthogonal axes, such as Cartesian coordinates. Theseaxes may be defined as a control line axis and an orthogonal axis, whereeach initial routing may be substantially parallel to the control lineaxis. Routing constraints and port locations may be taken from acomponent placement generated using the methods described in previoussections, or a component placement generated from any auto-place and-route tool.

2. Determining an Initial Routing

FIG. 9B shows a flow process diagram of one embodiment of a method fordetermining an initial routing for each control line based on therouting constraints and the port locations, each initial routing beingsubstantially straight (block 920). The method may include: (1)determining a length for each initial routing based on a distance alongthe control line axis between a first and second port locations (block922); and (2) determining a position for each initial routing based onan average distance orthogonal to the control line axis between at leastthe first and second port locations (block 924). The method may furthercomprise: (3) determining an alternate position for each initial routingwhere a blockage is present (block 926).

Each of the port locations may be associated with a first coordinatealong the control line axis and a second coordinate orthogonal to thecontrol line axis. Determining a length for each initial routing (block922) may include calculating a difference of the first coordinatesassociated with the first and second port locations. Determining aposition for each initial routing (block 924) may include calculating anaverage of the second coordinates associated with at least the first andsecond port locations.

If Cartesian coordinates are used, determining a length for each initialrouting (block 922) may include calculating a difference of the xcoordinates associated with the first and second control line portlocations. Determining a position for each initial routing (block 924)may include calculating an average of the y coordinates associated withthe first and second port locations and possibly other port locations.

Blockages may arise where the space or track needed for the initialrouting has already been used, such as for a previous routing.Determining an alternate position for each initial routing where ablockage is present (block 926) may include defining a search regionbased on at least the first and second port locations, and thenselecting a closest available position located within the search region.The search region may be a rectangular routing window which has at leasttwo corners defined by the first and second port locations. For example,the routing window may have diagonally opposing corners defined by thefirst and second port locations. The alternate position may be selectedby first looking to tracks immediately adjacent to the average position.

3. Determining a Cleanup Routing

FIG. 9C shows a flow process diagram of one embodiment of a method fordetermining a cleanup routing for each port location based on theinitial routing, the routing constraints, and the port locations, thecleanup routing connecting the initial routing for each control line toports associated with each control line (block 930). The method mayinclude: (1) determining a length for each cleanup routing based on adistance between the initial routing and the port location (block 932);and (2) determining a position for each cleanup routing based on theinitial routing and the port location (block 934). The method mayfurther comprise: (3) determining an alternate position for each cleanuprouting where a blockage is present (block 936). An external routernormally used as part of an auto-place and -route tool may be used toperform cleanup routing.

Determining a length for each cleanup routing based on a distancebetween the lo initial routing and the port location (block 932) mayinclude finding the shortest distance between the initial routing andeach port. Determining a position for each cleanup routing based on theinitial routing and the port location (block 934) may includepositioning the cleanup routing to connect the initial routing and eachport.

Blockages may arise where the space or track has already been used, suchas for a previous routing. Determining an alternate routing for eachcleanup routing where a blockage is present (block 936) may includegenerating a cleanup routing around the blockage. The alternate routingmay be selected by first looking to tracks immediately adjacent to theshortest routing, and then determining the shortest Manhattan lengthfrom the initial routing to each port.

EXAMPLE 3

FIGS. 9D-9K show one example of a method for determining a control linerouting for components of an integrated circuit. FIG. 9D shows aplacement of components 950 of an integrated circuit. The placementincludes information about the individual placement of each component950. Components 950 may be of different sizes, abut or overlap eachother, and/or be spaced at varying distances from each other. Components950 may each have one or more ports 952 to be connected to the controlline. The routing constraints and port locations may be part of theplacement information, or separate.

FIG. 9E shows an initial routing 960 for the control line. Initialrouting 960 is substantially straight, and parallel to a control lineaxis, which is coincident to the x-axis as shown in the figures. Thelength of initial routing 960 is determined along the control line axis,based on the locations of the two furthest ports 952 for this particularsection of the control line. The position of initial routing 960 is.determined along an axis orthogonal to control axis, which is coincidentto the y-axis as shown in the figures. The position of initial routing960 is determined by calculating an average of the y-values of thelocations of ports 952. This approach minimizes the length of thecleanup routing.

FIG. 9F shows a blockage 956 present and interfering with initialrouting 960. A search region 958 is then created, in this case arectangular region which uses ports 952 to define its comers. FIG. 9Gshows an alternate position for initial routing 960 selected to avoidinterference with blockage 956. Initial routing 960 is moved by lookingto the tracks immediately adjacent to blockage 956. For example, thetracks immediately to the top and the bottom of blockage 956 may besearched and their availability determined. Initial routing 960 may bemoved to still minimize the lengths of the cleanup routing in view ofblockage 956.

FIG. 9H shows initial routing 960 complete and ready for cleanuprouting. FIG. 91 shows cleanup routing 970 which connects initialrouting 960 to each of ports 952. In general, cleanup routing 970 isselected to be the shortest distance from initial routing 960 to each ofports 952. A blockage 956 interferes with one section of cleanup routing970. FIG. 9J shows an alternate routing for this section of cleanuprouting 970 to circumvent blockage 956. FIG. 9K shows both initialrouting 960 and cleanup routing 970 complete.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in this art.The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A computer implemented method for forming arelative placement of components of an integrated circuit from a netlistcomprising: taking a netlist representation of components forming all orpart of an integrated circuit; forming groups of components within thenetlist which have at least a selected degree of structural similaritybetween each other; making a structural similarity group which includesthose groups of components identified as having at least the selecteddegree of structural similarity; performing an initial relativeplacement of the groups of components; reducing wire lengths betweencomponents of initial relative placement; and adding to the relativeplacement those components from the netlist which were not included inthe groups of components.
 2. A method according to claim 1 wherein thestep of forming groups of components having at least a selected degreeof structural similarity between each other includes forming groups ofcomponents which include at least two components.
 3. A method accordingto claim 1 wherein the step of forming groups of components having atleast a selected degree of structural similarity between each otherincludes forming groups of components which include at least threecomponents.
 4. A method according to claim 1 wherein the step of forminggroups of components having at least a selected degree of structuralsimilarity between each other includes forming groups of componentswhich include at least four components.
 5. A method according to claim 1wherein the step of forming groups of components having at least aselected degree of structural similarity between each other includesforming groups of components having at least 10% similarity in bus lineand control line connectivity between components of the group.
 6. Amethod according to claim 1 wherein the step of forming groups ofcomponents having at least a selected degree of structural similaritybetween each other includes forming groups of components having at least20% similarity in bus line and control line connectivity betweencomponents of the group.
 7. A method according to claim 1 wherein thestep of forming groups of components having at least a selected degreeof structural similarity between each other includes forming groups ofcomponents having at least 33% similarity in bus line and control lineconnectivity between components of the group.
 8. A method according toclaim 1 wherein the step of forming groups of components having at leasta selected degree of structural similarity between each other includesforming groups of components having at least 50% similarity in bus lineand control line connectivity between components of the group.
 9. Amethod according to claim 1 wherein the step of forming groups ofcomponents having at least a selected degree of structural similaritybetween each other includes forming groups of components having at least66% similarity in bus line and control line connectivity betweencomponents of the group.
 10. A method according to claim 1 wherein thestep of forming groups of components having at least a selected degreeof structural similarity between each other includes forming groups ofcomponents having at least 75% similarity in bus line and control lineconnectivity between components of the group.
 11. A method according toclaim 1 wherein the step of forming groups of components having at leasta selected degree of structural similarity between each other includesforming groups of components having at least 80% similarity in bus lineand control line connectivity between components of the group.
 12. Amethod according to claim 1 wherein the netlist indicates an order forbus lines in the circuit, the step of performing an initial relativeplacement of the groups of components includes conserving the order ofbus lines indicated in the netlist.
 13. A method according to claim 12further comprising modifying the relative placement of componentsincluding conserving the order of bus lines indicated in the netlist.14. An integrated circuit design tool comprising: a processor; andmemory coupled to the processor including instructions which whenexecuted by the processor takes a netlist representation of componentsforming all or part of an integrated circuit and performs the followingsteps forming groups of components within the netlist which have atleast a selected degree of structural similarity between each other,making a structural similarity group which includes those groups ofcomponents identified as having at least the selected degree ofstructural similarity, performing an initial relative placement of thegroups of components, reducing wire lengths between components ofinitial relative placement, and adding to the relative placement thosecomponents from the netlist which were not included in the groups ofcomponents.
 15. A design tool according to claim 14 wherein the step offorming groups of components having at least a selected degree ofstructural similarity between each other includes forming groups ofcomponents which include at least two components.
 16. A design toolaccording to claim 14 wherein the step of forming groups of componentshaving at least a selected degree of structural similarity between eachother includes forming groups of components which include at least threecomponents.
 17. A design tool according to claim 14 wherein the step offorming groups of components having at least a selected degree ofstructural similarity between each other includes forming groups ofcomponents which include at least four components.
 18. A design toolaccording to claim 14 wherein the step of forming groups of componentshaving at least a selected degree of structural similarity between eachother includes forming groups of components having at least 10%similarity in bus line and control line connectivity between componentsof the group.
 19. A design tool according to claim 14 wherein the stepof forming groups of components having at least a selected degree ofstructural similarity between each other includes forming groups ofcomponents having at least 20% similarity in bus line and control lineconnectivity between components of the group.
 20. A design toolaccording to claim 14 wherein the step of forming groups of componentshaving at least a selected degree of structural similarity between eachother includes forming groups of components having at least 33%similarity in bus line and control line connectivity between componentsof the group.
 21. A design tool according to claim 14 wherein the stepof forming groups of components having at least a selected degree ofstructural similarity between each other includes forming groups ofcomponents having at least 50% similarity in bus line and control lineconnectivity between components of the group.
 22. A design toolaccording to claim 14 wherein the step of forming groups of componentshaving at least a selected degree of structural similarity between eachother includes forming groups of components having at least 66%similarity in bus line and control line connectivity between componentsof the group.
 23. A design tool according to claim 14 wherein the stepof forming groups of components having at least a selected degree ofstructural similarity between each other includes forming groups ofcomponents having at least 75% similarity in bus line and control lineconnectivity between components of the group.
 24. A design toolaccording to claim 14 wherein the step of forming groups of componentshaving at least a selected degree of structural similarity between eachother includes forming groups of components having at least 80%similarity in bus line and control line connectivity between componentsof the group.
 25. A design tool according to claim 14 wherein thenetlist indicates an order for bus lines in the circuit, the step ofperforming an initial relative placement of the groups of componentsincludes conserving the order of bus lines indicated in the netlist. 26.A design tool according to claim 25 further comprising modifying therelative placement of components including conserving the order of buslines indicated in the netlist.
 27. An article of manufacture comprisinga computer readable medium bearing a program code embodied therein forperforming a method for forming a structural similarity group from anetlist of an integrated circuit, the method comprising: taking anetlist representation of components forming all or part of anintegrated circuit; forming groups of components within the netlistwhich have at least a selected degree of structural similarity betweeneach other; making a structural similarity group which includes thosegroups of components identified as having at least the selected degreeof structural similarity; performing an initial relative placement ofthe groups of components; reducing wire lengths between components ofinitial relative placement; and adding to the relative placement thosecomponents from the netlist which were not included in the groups ofcomponents.
 28. An article of manufacture according to claim 27 whereinthe netlist representation includes all of the components formingintegrated circuit.
 29. An article of manufacture according to claim 27wherein the netlist representation includes a portion of the componentsforming integrated circuit.
 30. An article of manufacture according toclaim 27 wherein each group of components formed includes at least twocomponents.
 31. An article of manufacture according to claim 27 whereineach group of components formed includes at least three components. 32.An article of manufacture according to claim 27 wherein each group ofcomponents formed includes at least four components.
 33. An article ofmanufacture according to claim 27 wherein the selected degree ofstructural similarity is at least 10% similarity in bus line and controlline connectivity between components of the group.
 34. An article ofmanufacture according to claim 27 wherein the selected degree ofstructural similarity is at least 20% similarity in bus line and controlline connectivity between components of the group.
 35. An article ofmanufacture according to claim 27 wherein the selected degree ofstructural similarity is at least 25% similarity in bus line and controlline connectivity between components of the group.
 36. An article ofmanufacture according to claim 27 wherein the selected degree ofstructural similarity is at least 33% similarity in bus line and controlline connectivity between components of the group.
 37. An article ofmanufacture according to claim 27 wherein the selected degree ofstructural similarity is at least 50% similarity in bus line and controlline connectivity between components of the group.
 38. An article ofmanufacture according to claim 27 wherein the selected degree ofstructural similarity is at least 66% similarity in bus line and controlline connectivity between components of the group.
 39. An article ofmanufacture according to claim 27 wherein the selected degree ofstructural similarity is at least 75% similarity in bus line and controlline connectivity between components of the group.